Fiber optics are widely used as a medium for transmitting voice and data signals. As a transmission medium, light provides advantages over traditional electrical communication techniques. For example, light signals allow for relatively high transmission rates as well as for transmission over great distances without signal loss, and light signals are resistant to electromagnetic interferences that can interfere with electrical signals.
Optical communications systems present a number of implementation challenges. For example, the data carried by light signal must be converted from an electrical signal to light at the sending device, and then converted from light back to an electrical signal at the receiving device. Thus, in an optical communication system, it is typically necessary to couple an optical fiber to an opto-electronic transmitter, receiver or transceiver device and to, in turn, couple the device to an electronic system such as a switching system or processing system.
These connections can be facilitated by modularizing the transceiver device used at both the sending and receiving device. Various transceiver module configurations are known for interfacing with a host device, such as a host computer, switching hub, network router, switch box, computer I/O and the like. For example, the optical transceiver module 10 illustrated in partially disassembled form in FIG. 1 has a standard configuration or form commonly referred to as a Small Form-Factor (SFF) or SFF-Pluggable (SFP) format. Transceiver module 10 includes a metallic module housing shown in FIG. 1 as upper housing portion 12a and lower housing portion 12b in which are housed opto-electronic elements, optical elements 14, and electronic elements 16, such as one or more light sources (e.g., lasers), light sensors, lenses and other optics, digital signal driver and receiver circuits, etc.
The front end of transceiver module 10 further includes a transmitter receptacle 18 and a receiver receptacle 20 into which optical fiber cables (not shown) are pluggable. The optical cable plug or connector body (not shown) can be any of the standard type known in the field. The rear end of the transceiver module 10 typically has a plug portion 22 with electrical contacts 24 located thereon. As shown in FIG. 2, a transceiver module 10 can be plugged into a bay 32 in the chassis or cage 34 of an electronic system 30 by inserting the plug end 22 of transceiver module 10 into a bay 32 opening in the cage 34 and latching transceiver module 10 in place by any of a variety of know methods. The cage 34 is typically attached to a PCB 36, which is also part of the electronic system 30. The PCB 36 typically contains electrical interconnections (not shown) that come into contact with the electrical contacts 24 located on the plug end 22 of the electrical assembly 16 when the transceiver module 10 is inserted into the bay 32 of the cage 34.
Transceiver module size is of concern in the art. The width of housing 12a and 12b is substantially dictated by the two side-by-side receptacles 18 and 20. That is, housing 12a and 12b is at least as wide as the two connectors. Multiple transceiver modules of this type can thus be plugged into a cage panel at a pitch on the order of about every one-half inch. International and industry standards have been adopted that define the physical size and shape of optical transceiver modules to insure compatibility between different manufacturers, including the standards set forth in the Small Form-Factor Pluggable Transceiver Multisource Agreement. This standard defines not only the details of the electrical interface with compliant transceiver modules, but also the physical size and shape for compliant transceiver modules, and the corresponding module cage mounted on a printed circuit board for receiving the transceiver modules.
As the protocols used in optical networks increase in transmission speed, the heat generated by the transceivers typically increases, especially for smaller transceiver modules. For instance, 10-Gigabit transceivers generally require heat dissipation mechanisms. Thus, transceiver module cooling is a concern in the art. The heat emitted by the electronics and opto-electronics in a transceiver module 10 such as that shown in FIG. 1 and FIG. 2 is commonly conducted away from transceiver module 10 by metallic portions of the cage 34 in which transceiver module 10 is plugged.
Heat sinks can be included on the outside of the transceiver module 10 housing 12a and 12b and/or attached to the top surface of the cage 34 to dissipate this heat. However, such external heat sinks are inefficient as they cool all internal components of the transceiver module 10 to roughly the same temperature. Such external heat sinks do not allow for focused cooling of the internal components of the transceiver module 10 with lower operating temperatures, while not cooling internal components having maximum allowed operating temperatures.
Additionally, conventional external heat sinks provide design challenges in instances in which many transceiver modules are arranged closely together in connected cages. One such design challenge is that a conventional heat sink mounted to the top surface of the cage 34 prevents stacking transceiver modules on top of each other because only the uppermost transceiver module 10 is in contact with cage 34 and thus only the uppermost transceiver module 10 receives adequate heat dissipation. Thus, typical cages 34 allow for several transceiver modules 10 to be located side-by-side in the horizontal direction, but only allow for one transceiver module 10, or at most, two transceiver modules 10 to be stacked in the vertical direction.